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Elephants are known for their impressively long trunks, but
perhaps less well known is the large number of genes that code
for their sense smell.

In a study of 13 mammals, African
elephants were found to be superior sniffers, possessing the
largest number of genes associated with smell — five times as
many as humans and more than twice that of dogs.

The findings support other research on the pachyderm's superior
sense of smell. African elephants can smell the difference
between two tribes living in Kenya: the Maasai, whose young men
prove their virility by spearing elephants, and the Kamba,
farmers who usually leave elephants alone, reported a 2007 study
published in the journal Current
Biology.

Elephants also use their sensitive sense of smell to forage for
food and identify family members. Female African elephants are
only able reproduce for a few days every three years, and
research suggests that males can smell when a female is receptive
to reproduction, said Bruce Schulte, head of the department of
biology at Western Kentucky University in Bowling Green, who was
not involved in the study.

"When you watch the animal, even in captivity, the trunk is
constantly moving. It's constantly checking out the environment,"
Schulte told Live Science.

In the study, the researchers looked at the number of olfactory
receptor genes in each mammal. These genes code proteins that
reside in the nasal cavity and bind to odor molecules. Nerve
cells then relay the information to the brain, which classifies
the smell.

The number of olfactory receptor genes ranged from 296 in
orangutans to 1,948 in African elephants, the researchers found.
An analysis showed that the common ancestor of all 13 mammals had
781 such genes. This indicates that the number of olfactory
receptor genes has increased over time in elephants and rodents,
while it has decreased in primates, including humans who have 396
such receptor genes.

Genes increase through gene duplication, when one gene becomes
two, for example after an error in
DNA replication, Niimura said. When this happens, each gene
can acquire different mutations, and the genes eventually become
distinct from one another. Individuals can also lose genes if
mutations render them useless.

The primates in the study lost more than half of their olfactory
receptor genes. Most notably, orangutans lost about 70 percent
since the common ancestor lived about 100 million years ago.

"This study is a great step towards the identification of genes
related to olfaction stemming from the increasing number of
sequenced mammalian genomes," said Sergios-Orestis Kolokotronis,
an assistant professor of biology at Fordham University in New
York City, who was not involved in the study.

The study researchers did not examine the function of each gene,
but the vast number of olfactory receptor genes in the African
elephant suggests that its trunk has profound smelling abilities.